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Libet's Experiment

Review​

The neurophysiological experiments of Benjamin Libet and his collaborators in the 1980s -- The unconscious initiation of a freely voluntary act -- have been interpreted by the authors and many others as showing that our brains initiate conscious voluntary movements as well as the will to move before we are consciously aware of the will to move.

  • Cartesian dualism predicts that mind events should precede brain events, since the nonphysical mind (or soul etc.) is considered to be the real source of our decisions.
  • Two-aspect monism and mind-brain identity theory both predict that mind and brain events should be synchronous, since mind-level descriptions and brain-level descriptions are considered complementary (and equally valid) accounts of the same processes.
  • But if brain events come first, this might support epiphenomenalism, the view that mind events are mere by-products of brain events, with no causal role. This would deny the causal efficacy of conscious will.

In 2008, Soon et al ran a similar experiment made a summary claim that "decision can be encoded in brain activity of prefrontal and parietal cortex almost 10 sec before it enters awareness." The body of the paper explains that it was only 60% prediction accuracy, which casts doubt on the 10 second figure, however it seems at least that some activity happens a couple of seconds before we are aware of it.

Commentary​

Libet's conclusions always seemed a bit odd to me. What it shows is that we are not immediately aware of the decisions we make. Understand that thinking is distributed through the brain. Thinking is the activation of neural patterns. There is some part of the brain where activation of a neuron is the essence of making the decision. Being aware of a decision is a different thing. Being aware is activation of nerves that represent the language center so that it can communicate out that the decision has been made. When a person verbally confirms "knowing" that the decision has been made, that is specifically related to what the verbal center knows. The verbal center can not report knowing something until AFTER the verbal center is notified that the decision nerves are now active.

You can't "know you made a decision" BEFORE you actually make the decision. Because the nerves themselves are doing the thinking, and there can be no thinking that is not the activation of the nerves. The activation of the nerves to make the decision has to be the act that we normally think of as "making the decision". The awareness of the activation of those nerves HAS to be after they are activated.

Libet's results seem to me not at all surprising. What I don't understand is why people find it surprising. Some people conclude that these results mean that the person did not really make the decision, but that is silly. It means only that the ability to report having made the decision follows the decision by a fraction of a second. The brain is distributed, and all parts of the brain simply can not be aware of all other parts of the brain. We should not be surprised that there is some transmission delay.

Why would anyone expect the conscious experience of a decision to come at the same time as making the decision? What could it mean to "experience" the decision? Nothing is instantaneous.

References​

  • Libet, B., Gleason, C.A., Wright, E.W. & Pearl, D.K. ‘Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). The unconscious initiation of a freely voluntary act’, Brain (1983) 106: 623- 642.

  • Soon, C.S., Brass, M., Heinze, H.J. & Haynes, J.D. ‘Unconscious determinants of free decisions in the human brain’, Nature Neuroscience (2008) 11: 543-545.